1. Field of the Invention
This invention relates to article surveillance systems and more particularly it concerns novel methods and apparatus for deactivating targets used in such systems.
2. Description of the Prior Art
Magnetic type surveillance systems for protecting articles from theft are shown and described in French Pat. No. 763,687 and in U.S. Pat. Nos. 4,118,693, 4,326,198 and 4,384,281. As described in those patents, targets which are affixed to protected articles are made up of thin elongated strips of highly permeable, easily saturable magnetic material such as permalloy. Also, as described in U.S. Pat. Nos. 3,747,086, 3,820,103 and 3,820,104, the targets can be made deactivatable by providing them with deactivation elements of a high coercivity, magnetically hard material, such as vicalloy, which can be magnetized to provide spaced apart north and south magnetic poles which are effective to break up the magnetic continuity of the target strips. The deactivation elements are magnetized and demagnetized by subjecting them to a powerful magnetic field generated by a deactivating and reactivating machine at a checkout or authorizing station.
Pending U.S. patent application Ser. No. 513,242 filed July 13, 1983 discloses a deactivatable target which comprises a long continuous strip of permalloy material and a colinear continuous deactivation strip extending along the length of the permalloy strip. The deactivation strip is of a magnetically hard material such as vicalloy which is capable of being magnetized according to various patterns along its length. U.S. application Ser. No. 513,242 also discloses a permanent magnet deactivation assembly comprising a magnetizing strip or sheet having permanent magnets arranged therein with spaced apart alternate magnetic poles. When the target with its deactivation strip is placed along the deactivation assembly, the magnets therein cause the target's deactivation strip to become magnetized according to the pattern of the spaced apart alternate magnetic poles; and, as a result, the target's deactivation strip prevents the target from responding to an interrogation field when an article with the target attached to it is carried through the field.
The apparatus shown in U.S. patent application Ser. No. 513,242 also includes various arrangements for maintaining the target essentially parallel to the magnetizing strip or sheet and for guiding the target so that it is moved away from the magnetizing strip or sheet in a direction generally perpendicular thereto in order to maintain the pattern of magnetization imposed upon the target's deactivation strip by the deactivation assembly.
U.S. Pat. No. 4,568,921 shows an alternate form of target wherein the target strip comprises a wire of soft magnetic material such as permalloy and wherein the deactivation strip comprises one or more wires of hard magnetic material such as vicalloy.